A temperature inversion in WASP-33b?⋆,⋆⋆
Large Binocular Telescope occultation data confirm significant thermal flux at short wavelengths
1 Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: cessen@phys.au.dk
2 Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
3 N. Copernicus Astronomical Centre, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
4 Institut für Astrophysik Göttingen, Friedrich-Hund-Platz 1, 33037 Göttingen, Germany
Received: 27 March 2015
Accepted: 10 July 2015
We observed a secondary eclipse of WASP-33 b quasi-simultaneously in the optical (~0.55 μm) and the near-infrared (~1.05 μm) using the 2×8.4 m Large Binocular Telescope. WASP-33 is a δ Scuti star pulsating with periods comparable to the eclipse duration, making the determination of the eclipse depth challenging. We use previously determined oscillation frequencies to model and remove the pulsation signal from the light curves, isolating the secondary eclipse. The determined eclipse depth is ΔF = 1.03 ± 0.34 parts per thousand, corresponding to a brightness temperature of TB = 3398 ± 302 K. Combining previously published data with our new measurement we find the equilibrium temperature of WASP-33 b to be TB = 3358 ± 165 K. We compare all existing eclipse data to a blackbody spectrum, to a carbon-rich non-inverted model and to a solar composition model with an inverted temperature structure. We find that current available data on WASP-33 b’s atmosphere can be best represented by a simple blackbody emission, without the need for more sophisticated atmospheric models with temperature inversions. Although our data cannot rule out models with or without a temperature inversion, they do confirm a high brightness temperature for the planet at short wavelengths. WASP-33 b is one of the hottest exoplanets known till date, and its equilibrium temperature is consistent with rapid reradiation of the absorbed stellar light and a low albedo.
Key words: asteroseismology / techniques: photometric / occultations / stars: oscillations / planets and satellites: atmospheres / methods: observational
The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Instituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Leibniz-Institute for Astrophysics Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2015